Comparing formula methods of tree appraisal

Abstract

Values produced by formula methods of tree appraisal used in five different countries were compared (CTLA)-United States, Standard Tree Evaluation Method (STEM)-New Zealand, Helliwell-Great Britain, Norma Granada-Spain, and Burnley-Australia). Nine individuals appraised the same six trees using all five methods. The CTLA and Helliwell methods consistently produced the lowest values, and the Norma Granada method values were most often the highest. There was a strong relationship between variation among appraisers and the mathematical operations used in calculating the formula values. The Helliwell method, which multiplies all of the rated factors together, consistently produced the highest variation among appraisers. STEM, which adds all the factors together, consistently produced the lowest variation among appraisers. Minimizing the number of multiplication operations used in the formulas is an effective way of reducing appraiser variation, but in doing so, the influence of individual factors may be diminished too much.